The invertebrate chordates have some vertebrate characteristics such as a dorsal tubular nervous system and notochord. Among such phyla lacking a vertebral column occurs the Hemichordata. The class Pterobranchia of this phylum has not previously been explored with respect to biologically active or other chemical constituents.
In late 1972, we collected by SCUBA (ca. 20 m) in the Indian Ocean off Southeast Africa, in areas patrolled by the great white shark Carchorodon carchoris, specimens from this class of the marine worm (.about.5 mm long in tube colonies) Cephalodiscus gilchristi (order Cephalodiscida). Two years later, methanol and water extracts of C. gilchristi demonstrated a confirmed active level against the U.S. National Cancer Institute's murine P388 lymphocytic leukemia (PS system) and obtained a 32-41% life extension of 25-37.5 mg/kg. Now after more than fifteen years of relentless research directed at discovering the active constituent(s) of C. gilchristi, we have succeeded in the isolation and structural elucidation of a series of powerful cell growth inhibitory substances with PS cell line ED.sub.50 of 10.sup.-7 to 10.sup.-9 .mu.g/ml. Our early work resulted in four substances which were denominated "Cephalostatin 1", "Cephalostatin 2", "Cephalostatin 3", and "Cephalostatin 4" and form the subject matter of our prior U.S. Pat. No. 4,873,245. Additional information including the taxonomy of the Cephalodiscus gilchristie is available from: E. J. W. Barrington, The Biology of Hemi-chordata and Protochordata, W. H. Freeman and Co., San Francisco, 1965; and Cilchrist, J. D. F., 1915, "Observations on the Cape Cephalodiscus (C. gilchristi Ridewood) and some of its early sates", Ann. Mag. Nat. Hist., Ser. 8, 16, pp 233-246. Specimens of the C. gilcristi used by us were identified by the Museum National D'Histoire Naturelle, Paris, France in late 1977. Voucher specimens are on file at the Cancer Research Institute (CRI), Arizona State University, Tempe, Ariz. labelled M-1334 and GRP 8692. The specimens are available for inspection under the auspices of the Director of CRI.
The marine worm order Cephalodiscida (Hemichoradata phylum) contains two tube-living genera occurring primarily at considerable depths in the Southern hemisphere. Tubes containing colonies of these tiny marine animals are commonly found attached to marine life such as, bryozoans and sponges. Initial investigation of bioactive constituents in this worm class (Pterobranchia) by Pettit et al (J. Chem. Soc. Chem. Commun. 85 (1988) led to the discovery of a murine P388 lymphocytic leukemia (PS system) cell growth inhibitor denominated "Cephalostatin 1" in the South Africa (Indian Ocean) Cephalodiscus gilchristi. Subsequent isolation bioassays (PS) of C. gilchristi led to the isolation of two new and unusual disteroidal alkaloids bearing aromatic C-rings (shown above) which are herein designated "Cephalostatin 5" and "Cephalostatin 6." Both showed significant cell growth inhibition with P388 (PS ED.sub.50 10.sup.-3 and 10.sup.-2 .mu.g/ml), respectively.